The Important Role of Luminance and Chrominance in Noise Reduction

September 12, 2018

Choosing the best settings for noise filtration is a bit of a balancing act. In this process,
we tend to think of the screen as the final destination for our video content, but in reality
it is our eyes that are the final processor in the chain. Which means that understanding the
way our eyes work is critical to making good decisions when it comes to noise reduction. In
this three-part series of articles, we’ll examine the different components that make up
an image and the different ways our eyes perceive these components. We’ll explore the
important role of brightness (Luminance) and color (Chrominance) in noise reduction to help you
get better results.

Differences in visual sensitivity

Interestingly, scientific studies into human vision have revealed that we are not equally
sensitive to spatial variations in brightness and color. In fact, while we are very good at
picking up very fine details in brightness, we are actually less sensitive to fine spatial
changes of color. Knowing about these different sensitivities, we can use a smarter approach to
noise reduction.

RGB, YCbCr, Luminance & Chrominance

In video and photography, an image is often represented by a system called RGB, in which the
image is comprised of three color ‘channels’ - Red, Green and Blue. However, there
is another way that the picture can be represented called YCbCr. In this system, the Y is known
as the Luminance channel and it represents brightness within the image. While Cb and Cr are
Chrominance channels representing the color of the picture.

With separate control over each of these channels, video processors can apply different
treatments to take advantage of the difference in our sensitivity with regard to brightness and
color. For example, many video codecs separately compress the brightness and color channels to
achieve better overall compression without losing the fine details in the brightness
channel.

Neat Video also handles digital noise in YCbCr to approach noise reduction differently in the
Luminance and Chrominance channels.

Brightness, color and digital noise

When it comes to digital noise however, it gets more sophisticated. That’s because
digital noise in the Chrominance channels is also more objectionable to the human eye than
noise in the Luminance channel. In other words, while we can see digital noise in the Luminance
channel very well, it doesn’t bother us as much as noise in the Chrominance channels. We
should also take that into account when applying noise reduction.

This table shows the differences in human visual perception of brightness vs color in relation
to noise reduction:

Eye sensitivity to

Brightness (Luminance)

Color (Chrominance)

Fine details

very sensitive

less sensitive

Presence of noise

very sensitive;
less objectionable

very sensitive;
very objectionable

Loss of fine details
caused by noise reduction

very sensitive;
very objectionable

less sensitive;
less objectionable

Taking this into account, Neat Video’s noise reduction strategy is less aggressive for
Luminance and more aggressive for the Chrominance component of the image. This results in the
most pleasing interplay for our eyes.

Ok, so now that you know a little more about the relationship of Luminance and Chrominance to
noise reduction, we should discuss how these considerations can be used in practice when you
work with Neat Video. That’s the subject for the
next article!

See Also:

Video codecs treat data in Luminance and Chrominance channels differently, so should you when building noise profiles. This article will teach you how to utilize Neat Video's Profile Assist viewers to get closure to perfect noise-free videos.

Noise reduction might seem like magic, but there’s no secret mystery to achieving silky smooth video. In fact, sometimes simple changes can make a big difference to the end result. Here’s a few tips that will help you get those enchanting moving pictures.

When approaching the task of noise reduction, it helps to keep in mind that you have three important resources at your disposal. These are: knowledge, your time and your hardware. The way these things come together will help you to achieve better results, more rapidly.